Asthma is a prevalent, chronic inflammatory disease of the airways associated with a range of adverse health outcomes. Sleep difficulties are often viewed as a consequence of nocturnal awakenings due to nighttime asthma symptoms, which will resolve with appropriate treatment of asthma symptoms. However, insomnia symptoms occur even in those asthmatics without asthma-related nocturnal awakenings, thus representing comorbid insomnia. Our prior work suggests that insomnia can negatively impact asthma control by further limiting engagement in activities and quality of life and increasing the risk for future asthma exacerbations and need for emergency department visits and hospitalizations. Our proposed study adopts a novel perspective on the interaction between insomnia and asthma control: targeted treatments for insomnia could improve asthma control and reduce the burden of disease. We propose to test the efficacy of a Cognitive-Behavioral Treatment of Insomnia (CBT-I) intervention on sleep and asthma control in adults. We will compare two randomized interventions: (1) a self-guided, real-world applicable, Internet version of CBT-I, Sleep Healthy Using The Internet (SHUTi), and (2) an enhanced usual care (EUC), involving an educational video on insomnia. The aims of this proposed study are: (1) to compare the efficacy of SHUTi vs. EUC on sleep outcomes at 3 and 6 months after initiation of treatment in adults with asthma and comorbid insomnia, (2) to compare the efficacy of SHUTi vs. EUC on changes in asthma control from baseline to 3 and 6 months, and (3) to determine whether changes in sleep mediate the effects of treatment on asthma control at 3 and 6 months. Our exploratory aim is to determine whether changes in biomarkers of airway inflammation across 3- and 6-month follow-up account for the relationship between changes in sleep (from baseline to 3 months) and improvements in asthma control. The use of an efficacious, low cost, Internet-based, cognitive-behavioral intervention for insomnia can provide a treatment option that could be delivered in real-world clinical settings. Findings from our study could encourage the inclusion of insomnia?as a comorbid condition that affects asthma control, and should be identified and treated?into the current guidelines for the proper management of asthma.